(a) Field of the Invention
The present invention relates to a method for detecting a malfunction of cylinders in a car. More specifically, the present invention relates to a method for detecting a malfunction of cylinders in a car using a sensor that detects the oxygen content of the exhaust gas from the car.
(b) Description of the Related Art
In a multi point injection (MPI) car, fuel control is determined by considering the amount of air drawn into an engine,, and feedback from an oxygen sensor is used to more accurately control the air fuel ratio. However, since the outputs of the oxygen sensor do not distinguish between cylinders, differences in the volume of intake air between cylinders cannot be compensated for, and neither can fuel delivery abnormalities that result from faulty injectors. As the engine becomes worn, differences between cylinders become greater, and occasional misfires can occur. Currently, the cylinders are distinguished only when the misfires occur according to the OBD-2 method. In the event of a misfire, information such as the crank angular velocity variations can be used to determine the faulty cylinder since there are large variations, but in the event that a mixture is rich or lean, the cylinder in question cannot be distinguished.
Honda products use a wide range oxygen sensor to perform precise air fuel ratio control in a conventional engine, and other products adopt methods to measure ions at an ignition plug or determine the mixture using a pressure sensor.
The Honda products use an observer theory and the wide range oxygen sensor to reduce the nitrogen in the exhaust gas by 5%. However, the observer theory requires a great deal of computation and uses many resources of the engine electronic control unit (ECU). It is important to continually evaluate the oxygen content of the exhaust, and characteristics of the exhaust gas from each cylinder are required to distinguish faulty cylinders, so it is difficult to analyze and control the air fuel ratio for individual cylinders using a wide range oxygen sensor because of the number of computations involved.